1. Field of the Invention
This invention relates generally to gas combustion burners. More particularly, the present invention relates to an integral gas burner for a smoking article employing combustion for a pre-mixed gaseous fuel.
2. Description of the Related Art
Small scale gas combustion burners, such as those used in cigarette lighters, are well known in the art. Most cigarette lighters use buoyancy to entrain air for diffusion combustion. The fuel vapors and air meet at the point of ignition and burn instantaneously. Hence, the fuel and air are not mixed upstream from the point of ignition in such lighters. Since no apparatus for pre-mixing is necessary, a diffusion flame lighter may be quite short in length. Unfortunately, diffusion flame burners tend to produce soot from unburned hydrocarbons and pyrrolitic products that occur due to incomplete combustion of the gaseous fuel. Furthermore, flames produced by diffusion burners tend to be unstable and bend as the burner is rotated.
The production of a pre-mixed flame in a gas combustion burner is also well known in the art. A pre-mixed flame is the product of a combustion process wherein the fuel is mixed with air upstream of the point of ignition. By the time the fuel/air mixture reaches the point of ignition, a stoichiometrically sufficient amount of oxygen is available for the combustion reaction to proceed to near completion. The flame produced by the pre-mixing of the fuel and air is stable and will not bend if the burner is rotated. Furthermore, since the fuel/air mixture tends to combust completely, a pre-mixing gas burner produces little to no soot or unreacted hydrocarbons. The stoichiometric or oxygen-rich flame produced in such a gas burner leaves predominantly CO2, H2O and N2 as the only combustion byproducts.
In the production of a pre-mixed flame, the mixing of the fuel and air prior to combustion is usually performed with a venturi, which draws air into the burner as fuel passes therethrough. However, the presence of an effective venturi tends to add to the overall length of the burner apparatus. In addition, the fuel mass flow rate requirement of the burner affects the overall size of the combination of the burner and fuel storage container. For example, the smallest fuel flow rate for a butane lighter that sustains a stable pre-mixed flame approaches approximately 0.71 mg/s. Reducing the fuel mass flow rate requirement thereby allows for a reduction in the overall size of the burner and fuel storage container. Reducing the size of the burner and fuel tank expands the scope of possible applications of such a burner.
It is, therefore, desirable to provide a gas burner that produces a stable pre-mixed flame and that is small enough to be used in a variety of applications, such as smoking articles.
It is an object of the present invention to provide a gas burner that generates a stable pre-mixed flame with low fuel mass flow rate requirements.
It is another object of the present invention to provide a gas burner that may be used for a smoking article and that also may be sized smaller than conventional gas lighters.
It is a further object of the present invention to provide a mixing chamber for a gas burner that provides highly efficient mixing of fuel and air in a small volume.
More particularly, the present invention is directed to a burner assembly for combustion of gaseous fuel. The burner assembly includes a fuel inlet, nozzle, an oxygenation chamber with at least one air inlet, a mixing chamber, at least one permeable barrier, a flame holder, an optional flame tube, and an optional burner housing. The fuel inlet connects the burner assembly to the gaseous fuel storage tank. An optional flow adjustment mechanism may be attached to the fuel inlet to regulate the fuel mass flow rate from a fuel storage container. The nozzle is in flow communication with the fuel inlet and affects both the static pressure and the velocity of the fuel stream passing therethrough. The nozzle feeds fuel from the fuel inlet to the oxygenation chamber. The inner diameter of the nozzle is significantly smaller than that of the fuel inlet, thereby accelerating the fuel stream passing therethrough. The static pressure of the fuel stream drops as it travels from the constricted nozzle into the larger oxygenation chamber. At least one air inlet is disposed in one or more of the walls of the oxygenation chamber. Air is drawn into the oxygenation chamber through the air inlet(s) by the reduction in static pressure caused by the gaseous fuel entering the oxygenation chamber through the nozzle. The size of the nozzle influences the mass flow rate of air drawn into the venturi tube through the air inlets.
A mixing chamber is in flow communication with the oxygenation chamber. The mixing chamber provides for the efficient mixing of the air and the gaseous fuel in a relatively small volume. The mixing chamber has either an inner wall which includes a frustoconical section, or a ferrule may be disposed within the mixing chamber to provide an inner wall with a frustoconical section. In either case, the interior of the mixing chamber expands from the proximal end, which is adjacent to the oxygenation chamber, to the distal end. The diverging side wall of the mixing chamber provides an interior space in which the fuel and air may efficiently mix. At least one permeable barrier is disposed downstream of and in flow communication with the mixing chamber. The permeable barrier may be disposed at the outlet of the mixing chamber to be spaced therefrom. The permeable barrier may be a porous metal or ceramic plate, or another permeable material or structure that inhibits the flow of the fuel/air mixture from the mixing chamber. The permeable barrier restricts the flow of the fuel/air mixture and causes a drop in the mixture""s static pressure. The result of the flow restriction is recirculation of a portion of the fuel/air stream within the mixing chamber. Recirculation eddies tend to form within the mixing chamber around the axis of the flow stream. This recirculation provides for a more complete mixing of the fuel/air stream prior to ignition.
A flame holder is disposed in the gas burner downstream of and in flow communication with the permeable barrier(s). The flame holder includes at least one opening therein which further restricts the fuel/air stream flow. An ignition means is disposed downstream of the flame holder and precipitates the combustion of the fuel/air stream upon activation. The flame holder prevents the flame generated by the combustion of the fuel/air stream from flashing back through the burner. An optional flame tube may also be provided. The flame tube localizes the flame and prevents diffusion of air to it. The flame generated by the burner is a stable pre-mixed flame that has at least a stoichiometrically sufficient amount of air for complete combustion of the fuel.
The flame generated within the gas burner will not bend and is, thus, unaffected by the orientation of the burner. Furthermore, the combustion process carried out in the burner does not require diffused air to assist in complete reaction; therefore, the flame may be enclosed within a flame tube. Enclosing the flame allows the gas burner to be employed in a variety of applications, such as an integral cigarette lighter, in which other flames, which rely on diffusing air, would be inappropriate. The burner generates a stable, pre-mixed flame with a significantly smaller fuel flow rate than required by conventional cigarette lighters. For example, conventional butane lighters generally required fuel mass flow rates of at least 0.71 mg/s, whereas the gas burner of the present invention produces a sustainable pre-mixed flame with a fuel flow rate in the range of approximately 0.14 mg/s-0.28 mg/s. At this specified range, a lighter utilizing the gas burner of the present invention generates a heat output of approximately 6-12 Watts. Such power output allows such a gas burner to be used in an integral lighter for a smoking article.
It will become apparent that other objects and advantages of the present invention will be obvious to those skilled in the art upon reading the detailed description of the preferred embodiment set forth hereinafter.